1. Chapter 13: Star Clusters Open cluster globular cluster Stars (almost) always form in clusters The stars all formed at the same time They are all at the same distance They formed from the same material Only difference is their masses!

2. h & Chi Persei – Double Cluster in Perseus

3. Messier 35 and NGC2158 – “open clusters” of different ages

4. Open clusters: 1.Contain < ~ 1000 stars 2.Loosely gravitationally bound together 3.Younger than globular (some still contain O and B stars) 4.More enriched in heavy elements (“Population I” stars) Pleiades

5. Messier 50 – An “open cluster” of stars

6. Open clusters that have become gravitationally unbound are stellar associations. If they continue to have similar proper motion, this is a moving group. Ursa Major moving group

7. globular clusters: 1.Contains ~1000-10 6 stars 2.Extremely old: billions of years 3.Population II (low in heavy elements)

8. “He who cannot see gravity at work here has no soul.” - Richard Feynman Globular cluster M2

9. HD Diagram for star clusters: only difference is mass

10. Isochrones: Lines of ‘constant age’ for stars of different masses

11. M.S. LIFETIME for STAR at TURNOFF = AGE of CLUSTER

12. StarStar cluster website

14. Star clusters are useful to: 1.Verify stellar evolution models 2.Determine distances to nearby galaxies 3.Determine chemical composition of universe in the very distant past